The following technology is, for example, known in relation to electrostatic protection circuits that protect semiconductor devices from electrostatic discharge (ESD).
Namely, an electrostatic discharge protection circuit is known that includes a first NMOS transistor and a second NMOS transistor that are inserted between an external connection pad and a ground connection line and connected together in series, a first gate potential control circuit, and a second gate potential control circuit. The first gate potential control circuit is connected to the gate of the first NMOS transistor, includes a capacitor element, sets the gate potential of the first NMOS transistor to the same potential as a power source line during normal operation, and makes the gate potential of the first NMOS transistor effectively the same as ground level when an electrostatic surge occurs. The second gate potential control circuit is connected to the gate of the second NMOS transistor, and makes the gate potential of the second NMOS transistor ground level during normal operation.
Another known semiconductor device includes a first MOS transistor connected between an input line and an internal node, and a second MOS transistor that is connected between a second power source line and the internal node, and that has a gate electrode connected to the second power source line. This semiconductor device further includes a circuit element that is provided between a first power source line and the gate electrode of the first MOS transistor, and that is capable of applying a control voltage when the first MOS transistor enters a normally ON state.
A stacked MOS transistor protection circuit is also known that is provided with first and second MOS transistors that have the source of the first MOS transistor and the drain of the second MOS transistors connected together. The stacked MOS transistor protection circuit includes a diode serving as a clamper circuit with a cathode connected to the gate of the first MOS transistor and an anode connected to the drain of the first MOS transistor.